<p>The primary objective of this study was to review a methotrexate 90-mg fixed-dose protocol for treatment of ectopic pregnancy, and to evaluate if any characteristics were associated with ectopic pregnancy treatment failure. This was a single arm retrospective cohort study conducted at Kaiser Permanente Colorado. The primary outcome was to describe rates of ectopic pregnancy treatment failure among patients who received fixed dose(s) of methotrexate for ectopic pregnancy between January 1, 2007 and August 31, 2017. Women were eligible for inclusion if they received outpatient treatment with methotrexate for an ectopic pregnancy during this time frame. Electronic administrative databases were queried to identify eligible patients and gather patient data, then patients were categorized based on success or failure of treatment. Ectopic pregnancy treatment failure was defined as the requirement for any additional intervention to terminate the pregnancy. A total of 259 patients were included in the final analysis. Overall, 210 (81.1%) ectopic pregnancies were successfully treated with methotrexate alone, and 49 (18.9%) required additional intervention. Baseline human chorionic gonadotropin (hCG) of less than 1000 mIU/ml was associated with treatment success (odds ratio for ectopic pregnancy treatment failure = 0.07 (95% confidence interval: 0.03-0.19)). Treatment of ectopic pregnancy with this fixed-dose methotrexate protocol is a reasonable alternative to weight-based dosing. Consistent with previously published studies, baseline hCG less than 1000 mIU/ml was associated with a high rate of treatment success.</p>